The present invention relates to the medical imaging arts. It particularly relates to three-dimensional angiography using the magnetic resonance imaging (MRI) and computed tomography (CT) medical imaging techniques, and will be described with particular reference thereto. However, the invention will also find application in conjunction with other three-dimensional or two-dimensional angiographic imaging modalities as well as in other imaging arts in which tubular structures and networks of non-uniform diameter are advantageously differentiated from extraneous imaged structures and background noise.
Catastrophic medical events such as heart attacks and strokes that result from underlying vascular problems are a leading cause of death in the United States. Many Americans also suffer from chronic vascular diseases which degrade quality of life.
Angiography, which relates to the imaging of blood vessels and blood vessel systems, is a powerful medical diagnostic for identifying and tracking vascular diseases. Angiography enables improved surgical planning and treatment, improved diagnosis and convenient non-invasive monitoring of chronic vascular diseases, and can provide an early warning of potentially fatal conditions such as aneurysms and blood clots.
Angiography is performed using a number of different medical imaging modalities, including biplane X-ray/DSA, magnetic resonance (MR), computed tomography (CT), ultrasound, and various combinations of these techniques. Two-dimensional or three-dimensional angiographic data can be acquired depending upon the medical imaging modality and the selected operating parameters. Many angiographic techniques employ invasive or contrast enhanced methodologies in which a contrast agent that accentuates the vascular image contrast is administered to the patient prior to the imaging session. For example, in MR imaging, a magnetic contrast agent such as Gadolinium-Dithylene-Triamine-Penta-Acetate can be administered. However, some techniques, such as MR imaging, are also capable of providing vascular contrast using non-invasive approaches, by taking advantage of aspects of the vascular system, particularly the blood motion or flow, to enhance the vascular contrast without an administered contrast agent. An example of such a methodology in MR imaging is the time of flight (TOF) technique in which the magnetic resonance excitation and the spin echo RF pulse are directed at different slices such that the magnetic resonance excitation of the flowing blood is selectively echoed.
Regardless of the imaging modality or technique, three-dimensional or volume angiographic imaging typically produces gray scale data comprised of voxels of varying intensity. Analysis and interpretation of the unprocessed gray scale angiographic image is complicated by a number of factors. Complexity arises because blood vessel networks in the human body are highly intricate, and a particular image will typically include tortuous or occluded blood vessels, shape variability, regions of very high blood vessel densities, a wide range of blood vessel diameters, and the like. Additionally, angiographic techniques, although designed to selectively image the vascular system, typically also include contrast due to non-vascular structures such as internal organs and bone tissue that can further obscure the imaging of the vascular system. The angiographic data acquisition itself also introduces imaging artifacts such as background noise and partial volume averaging.
The vascular contrast of the raw angiographic data is advantageously improved through post-acquisition data processing or filtering. However, past filtering methods have proven unsatisfactory for removing non-vascular structures due to the large variation in blood vessel diameters in typical angiographic data which makes distinguishing blood vessels from other body organs and bone tissue difficult. In the past, clinicians have resorted to manually removing identifiable non-vascular image portions. This approach is highly unsatisfactory because it is labor intensive and can result in the loss of valuable vascular information in the removed image regions.
The present invention contemplates an improved post-acquisition angiographic filtering system and method, which overcomes the aforementioned limitations and others.